TRANSCRANIAL DOPPLER ULTRASONOGRAPHY DURING HEAD-UPRIGHT TILT-TABLE TESTING

The patient described in this report had symptoms that were consistent with vasovagal syncope, that were reproduced during head-upright tilt-table testing, and that occurred despite the maintenance of systemic arterial pressure and in the absence of bradycardia. Transcranial Doppler ultrasonography identified a substantial decrease in mean cerebral blood flow velocity in the setting of cerebral arteriolar vasoconstriction when the patient became symptomatic. This suggests that the impaired cerebral autoregulation that occurs during vasovagal syncope may be manifested independently of the abnormal baroreceptor responses that usually accompany this disorder.